Centrifuge rotors of the swinging bucket type are well known. These rotors are typified by a central hub portion having arms radiating outwardly therefrom. The radially outward ends of the arms are typically somewhat enlarged to define a support portion adapted to receive the trunnion support pins on which the buckets are carried. The lateral surfaces of the enlarged support portion extend substantially vertically or parallel to the axis of rotation of the rotor. The trunnion pins are received in bores extending into the enlarged support portion. The axes of the pins on confronting surfaces of angularly adjacent arms are co-planar and extend toward each other along a substantially chordal line. Onto confronting pairs of these trunnion pins are mounted the swinging buckets which receive a container carrying the sample to be centrifuged. Suitable trunnion pockets are provided at predetermined locations on the bucket to effectuate the mounting of the bucket to the rotor. When the rotor is at rest the buckets depend vertically downwardly from the trunnion pin so that the axis of the bucket is substantially parallel to the rotational axis of the rotor. As the rotor is brought up to operating speed, however, the buckets pivot about the trunnion pins and swing radially outwardly under the influence of a centrifugal force field. That is, during operation the axis of the bucket is substantially perpendicular to the rotational axis of the rotor.
It is important that the support portions at the outward ends of each of the arms have a sufficient volume of material to adequately support the trunnion-receiving bores which extend thereinto from each lateral surface. With relatively large diameter rotors, or with smaller diameter rotors having a bucket-carrying capacity of four buckets or less, sufficient material is usually present in the support portions at the radially outer ends of each of the arms. Thus, providing trunnion-receiving bores into each lateral side of the support portion so that a sufficient volume of material remains to adequately support the trunnion pins may be relatively easily accomplished.
However, with small rotors and/or rotors having a capacity of greater than four buckets it is often difficult to arrange and locate the trunnion-receiving bores such that a sufficient volume of material remains in the support portion to adequately bear against the trunnion pins. If the trunnion-receiving bores on opposite sides of a rotor arm communicate with each other, the integrity of the support portion of the arm may be compromised.
One expedient for locating trunnion pins in small diameter and/or large capacity rotors is disclosed in U.S. Pat. No. 4,009,824, issued to Wright. This patent discloses a centrifuge rotor in which a single bore is formed in the radially outer support portion on each of the arms, the bore extending perpendicularly to the radial axis of the arm. A trunnion pin is received in each of the bores, each trunnion pin including an elongated central portion and having acutely oriented opposite extremities. When the trunnion pin is inserted into the bore the opposite extremities of each trunnion pin extending outwardly from the lateral surfaces of the arm coaxially towards the outwardly extending extremity of the pin disposed in an angularly adjacent arm to thereby form a pair of trunnion pins for receiving the bucket assembly.